1. Field of the Invention
This invention relates to a fire suppression system for enclosed spaces containing equipment, apparatus or materials that require protection from combustion hazards, such as a fire. In particular, the invention concerns an improved retrofitted fire suppression system and method in which the fire suppression agent is HFC 125 as a replacement for Halon 1301. The system and method also has utility for design and installation of new fire suppression equipment based on the use of HFC 125, in lieu of Halon.
Halon 1301 has long been used as a fire suppression agent for areas where utilization of water spray or mist, solid suppressants such as sodium bicarbonate, or liquified compressed carbon dioxide is precluded. Exemplary in this respect are rooms or enclosures containing computer or electronic equipment, which would be damaged by water impingement. Solid suppressant discharge is undesirable in these applications because of the powdered residue that would be left on such equipment. Carbon dioxide suppressant systems have the disadvantage that at levels of CO2 adequate to suppress a fire, the resultant displacement of air is such that the environment would potentially be unsafe for individuals in the protected area.
2. Description of the Prior Art
It has been the practice for many years to protect sensitive equipment such as computer installations, electronic components, and materials or devices that would be damaged if subjected to fire suppressants such as water, or a solid agent. A common suppressant such as CO2 is also ruled out because the carbon dioxide displaces air from the enclosed space to an extent that individuals in the protective zone are placed at risk for lack of required oxygen.
In order to meet the need for protecting computer rooms and the like from a fire hazard, it became the practice a number of years ago to use a fluorocarbon, such as Halon 1301 as the suppressant agent. Halon had the advantage of being storable as a liquid under pressure at room temperature and which vaporized to produce a fire suppressant gas when discharged into the enclosure or area to be protected. Halon 1301 was deemed to be a “clean” fire suppressant because upon discharge of the agent it did not damage the equipment being protected from a fire hazard. Furthermore, individuals were still able to breathe adequately in the room or enclosure into which the Halon was discharged because the suppressant agent was found to be effective at a concentration which would put out a fire in the enclosure while still leaving a breathable oxygen level in the protected area.
Because of the clean unique characteristics of Halon 1301 as a fire suppressant agent, which was effective at breathable concentrations, Halon suppressant agent installations became the de facto agent for all applications where discharge of water or solid suppressant, or use of CO2 as a suppressant was undesirable or impractical. Halon-based suppressant systems have been installed throughout the United States and in many countries abroad.
In recent years, there has been mounting evidence that certain fluorocarbons, including Halon 1301, when discharged into the atmosphere tend to rise and accumulate in the stratosphere, thereby producing a deleterious hole in the ozone level over Antarctica creating undesirable global environmental effects. Because of mounting scientific evidence of the detrimental effect on the environment caused by certain fluorocarbons, such as Halon 1301, countries around the world have banded together and approved treaties either banning the use of Halon 1301, or imposing substantial surcharges on the purchase and use of Halon 1301 in new installations, or in recharging of existing fire suppressant systems. The goal of the largely successful treaties has been to coerce manufacturers and users to abandon use of Halon 1301 as a suppressant agent or at least substantially reduce the population of existing Halon 1301 installations.
Replacement or retrofitting of Halon 1301 fire suppressant systems has been impeded by the difficulty of developing a reasonable substitute for Halon 1301 which is as effective in suppressing fires, that can be made available at a non-prohibitive cost, and that negates the necessity of completely replacing the piping and distribution components of existing fire suppression systems. Noteworthy in this respect is the fact that in a significant proportion of Halon based fire suppression systems installed to protect electronic equipment such as computer components, the piping for the suppression system is located beneath the floor supporting the equipment requiring protection. It therefore is largely impractical to remove the computer equipment, tear up the floor and disconnect all of the wiring to the electronic components, merely for the purpose of replacing the fire suppression system piping.
One substitute fluorocarbon that offered promise as a replacement for Halon 1301 was FM-200®, available from Great Lakes Chemical Company. Principal disadvantages of the use of FM-200® have been the higher product cost, and the need to use a larger quantity of the agent as compared with Halon 1301 for a similar area to be protected. This larger amount of FM-200® required that the receptacles for storing the suppressant agent be larger than those typically used for Halon 1301 to protect the same area, and the FM-200® had different physical properties and flow characteristics which did not necessarily permit use of that agent in an existing fire suppression system without modification of the distribution components and nozzles of the system.
The need to repipe a protected area such as a computer room to replace an existing Halon system with an FM-2000® system presented such a formidable and expensive undertaking that many users elected not to do so and if recharging of the system with Halon was necessary, users decided to pay the necessary excise fees to buy a replacement amount of Halon 1301. The problem presented by Halon 1301 replacement is exacerbated by the fact that it is desirable that a system be tested by discharge of the Halon from time to time to verify the operability of the system and its effectiveness. Each time a test discharge is carried out, replacement Halon 1301 has to be purchased for recharging the system even though the Halon 1301 can be obtained only at what amounts to a largely prohibitive higher cost than the initial cost.
In certain jurisdictions, with Europe being a particular example, recently enacted legislation bars manufacture and sale of Halon 1301 for fire suppression applications in European Union countries. Therefore, replacement of Halon 1301 with a Halon recharge is simply not an option.
Halon 1301 has been stored as a pressurized gas within a pressure vessel in which pressurized nitrogen was contained in the vessel interior above the level of the liquified suppressant agent therein to assure complete delivery of the liquid suppressant agent through the system piping to the nozzles so that the time of discharge of the agent was maintained in the approved time range of 6 to 10 seconds.
Another fire suppressant fluorocarbon proposed as a substitute for Halon 1301 and that does not exhibit the undesirable ecological effects of Halon 1301 is HFC-125. However, use of HFC-125 also has the disadvantage vis a vis Halon 1301 of requiring delivery of a greater amount of the suppressant agent to meet standardized fire suppression tests.
The vapor pressure of Halon 1301 is about 200 psi. However, HFC-125 has a substantially lower vapor pressure, of the order of 125 psi. Accordingly, even if an atmosphere of relatively high pressure nitrogen is provided in overlying relationship to the pressurized liquified suppressant agent in the supply vessel as an aid in delivery of the liquified agent through the piping distribution array, HFC-125 will not flow through such piping at the same rate as is the case with Halon 1301. A HFC-125 system therefore inherently flows slower than a comparable Halon 1301 system.
As a consequence, the specific piping components and arrangement of a particular existing Halon 1301 fire suppression system have a different effect on the overall flow rate of HFC-125 as compared with Halon 1301 suppression agent. Elbows and tees in the piping system are known to have a pronounced effect on flow rates and how the liquid divides one way or the other at a bullhead or a side through tee. Simply adding additional pressure to the liquified HFC-125 in the storage vessel in the form of higher pressurized nitrogen, in an effort to solve the problem of the inherently slower flow rate of HFC-125 as compared with Halon 1301, is not feasible because of the problem of choked flow.
Computer programs have been developed and are available for evaluating the flow characteristics in specific storage vessels, piping and nozzle systems for delivery of liquified gaseous suppressant agents, including pressurized liquefied carbon dioxide, Halon 1301, HFC227ea (FM200) and HFC223 (FE13). The programs take into account factors such as pipeline pressure and agent density in the pipeline, pressure drop along the length of the piping system, turbulence, velocity changes, transients, mechanical effects on density and flow such as occur through an elbow, a bullhead tee or side-through tee, and the internal surface of the pipe sections and connectors. These computer programs have been used by installers of pressurized liquefied gaseous suppressant agents to determine the amount of a particular agent required for a given amount of area to be protected, the piping system necessary for such system, the number, size and location of nozzles and the pressurized nitrogen head required over the stored liquefied suppression agent.
The computer programs contained mathematical correlations and look up tables that gave the installer of a system substantial assurance full discharge of the liquefied suppression agent from the fire protection system would occur in a time range meeting approved regulations or standards, with a built in safety factor, usually in the range of about 20% in the United States to about 30% in Europe.